Microstructure,Properties And Cold Heading Forming With Its Finite Element Simulation Of TC16 Titanium Alloy Bar

TC16 titanium alloy has the advantages of good cold heading plasticity,high strength and good hardenability.It can be cold headed in the annealed state,which effectively reduces production costs and improves production efficiency.It is one of the ideal materials for manufacturing aviation fasteners.However,the domestic TC16 titanium alloy still has problems such as unsatisfactory yield of cold heading.Therefore,it is of great practical significance to carry out research on the structural properties of TC16 titanium alloy and the parameters of cold heading.In this paper,the TC16 titanium alloy is taken as the research object,the microstructure evolution of the bar during the preparation process,as well as the microstructure and cold heading performance after annealing are studied,and the influence of different cold heading process parameters on its forming performance is studied using finite element analysis software.The main research contents and conclusions are as follows:The microstructure evolution of TC16 titanium alloy bar during the preparation process was studied.The results show that the structure of the TC16 titanium alloy ingot is a basket structure composed of lamellar ? phase and ? matrix;the microstructure of the hot forging billet is locally inhomogeneous,the small and disordered equiaxial and laminar ? phases coexist in the local of forging billet;the microstructure of the hot-forged bar is composed of coarse ?+? near-equiaxed grains;the microstructure of the hot-rolled bar is characterized by small and dense spherical ?-phase uniformly distributed on the ? matrix.After annealing treatment of TC16 titanium alloy bar(annealing temperature 760~780?;holding time 2h;air cooling after furnace cooling to 550?),the microstructure is composed of uniformly distributed equiaxed ? phase and intergranular ? phase.The tensile fracture has the characteristics of ductile fracture,the tensile strength is 880~895MPa,the yield strength is 840-850 MPa,the elongation is 24~25%,the section shrinkage is 61.6~64.5%.When the deformation amount of the cold heading sample is 75%,the surface has no cracks and other defects,which can meet the cold heading requirements of fasteners.The effects of different cold heading process parameters on the forming properties of TC16 titanium alloy were studied with DEFORM-3D software.The results show that the maximum equivalent strain increases with the increase of the friction coefficient,and increases first and then decreases with the increase of the deformation speed;the maximum equivalent stress increases with the increase of the friction coefficient,and decreases first and then increases with the increase of the deformation speed;the billet temperature increases with the increase of the friction coefficient or the deformation speed;the cold heading load increases with the increase of the friction coefficient or the deformation speed,and friction coefficient has the greatest influence on cold heading load.The TC16 titanium alloy bar cold heading process parameters were improved through analysis.The structure and performance of the specimen after cold heading deformation showed a certain degree of unevenness.A double-fork deformed shear band appeared in the low-power tissue,and the hardness test results showed that the hardness value of the shear band area was higher than that of other parts.Through the finite element simulation,it is found that the area of the shear zone has the largest deformation and the highest temperature rise.The simulation results are in good agreement with the plastic deformation of the free upsetting sample.